Cataract surgery is one of the most common surgical procedures performed in the United States. The term "cataract" refers to any opacification of the natural crystalline lens in the eye. Cataracts cause loss of vision. Cataracts are commonly treated by surgically removing the lens from the eye and replacing the natural lens with an artificial lens that restores the vision.
The eye, or eyeball, is roughly spherical in shape. The shape of the eyeball is maintained by an opaque tissue membrane called the sclera, which constitutes the posterior five-sixths (5/6) of the eyeball. The cornea constitutes the remaining one-sixth (1/6) and is positioned at the anterior portion of the eye. The cornea is the transparent anterior portion of the eyeball that extends out from the globe forming a small dome. The outer surface of the cornea is protected by a layer of cells called the corneal epithelium. The bulbar conjunctiva (hereinafter conjunctiva) covers the sclera and is attached at the corneoscleral limbus. The cornea is essentially contiguous with the sclera and the transition from the sclera to the cornea is defined by the corneoscleral junction or limbus. The iris, the colored part of the eye, is a muscular diaphragm in front of the lends. The iris divides the chamber between the lens and the cornea into two chambers: the anterior chamber between the iris and the cornea, and the posterior chamber between the iris and the lens. The lens is held in position in the eyeball by the lens capsule and the lens has a nucleus in its center surrounded by cortex.
In order to remove a cataract, an entry or incision must be made into the eye. Typically, two incisions are made. The surgeon first makes a small incision (1.0 mm to 1.5 mm) through the cornea into the anterior chamber to introduce a protective gel (viscoelastic). This maintains the shape of the eye while protecting the posterior portion of the cornea.
The second incision is more complex and is typically 1.5 mm to 3.2 mm in width. The length of this incision varies from 1.75 mm to 3.0 mm, depending on surgeon preference and placement of the incision. The second incision begins with the conjunctiva being dissected with scissors to allow exposure of the sciera and placement of a groove. Hemostasis is performed using some type of cautery or diathermy. A groove is then made in the sclera. The sciera is then dissected into the cornea using some type of tunneling blade. At this point, a keratome or second surgical blade is introduced into the incision and entry is made through the cornea parallel to the iris, into the anterior chamber of the eye 92.5 mm to 3.2 mm). This incision allows the surgeon to remove the anterior capsule of the lens and, using a method of extraction called phacoemulsification, remove the nucleus of the lens.
Irrigation/aspiration is then used to remove the cortex, leaving the capsular bag in place. The incision is then enlarged and additional viscoelastic is introduced into the capsular bag (the lens membrane emptied of its nucleus and cortex material). The artificial lens is then implanted into the capsular bag and the viscoelastic is removed. The selera is sutured and the conjunctiva is tacked down using a cautery or diathermy.
A small number of surgeons have developed an advanced technique using a foldable intra-ocular lens and performing a clear corneal incision that eliminates the dissection, diathermy, the enlarging of the incision, and the suturing of the incision described. This technique promotes quicker visual recovery, decreases surgically introduced astigmatism and reduces operating time.
Typically, the clear corneal incision is made freehand, using a diamond or metal keratome of varying widths depending on the surgeons needs. A keratome is a surgical instrument consisting of a glade and a handle used for making an incision in the cornea. The blade is mounted on one end of the instrument and held by the surgeon at the other end. The width of an incision is determined by the dimensions of the blade mounted on the keratome. The length of the incision is determined by where the surgeon chooses to enter the anterior chamber.
To make a clear corneal incision under the prior art a surgeon uses two separate instruments, one held in each hand. The eye is fixated with one hand using forceps or other fixation devices such as a Fine-Thornton Fixation ring. The other hand holds the keratome to make a freehand incision in the eye. Because of the dome shape of the cornea, the surgeon must estimate the angle at which to introduce the keratome into the cornea. Too steep an angle will create an excessively long tunnel where it is difficult to maneuver instruments, and creates stria which makes it difficult to visualize. Too shallow an angle will create a very short tunnel which will not seal as well and may give pathogens such as bacterial access into the eye. The ideal incision would be located at the corneoscleral limbus and be 1.50 mm to 2.00 mm in length, self-sealing, and reproducible.
The incision guide of the present invention combines two prior art instruments into a single instruments and eliminates the guess work involved in determining the optimal angle at which to introduce the keratome into the cornea. The present incision guide places a keratome (or surgical blade) in optimal position at the corneoscleral limbus and at the optimal angle at which to introduce the keratome into the cornea.
Freehand surgery requires a very high skill level, entailing a training and transitional educational phase in which the surgeon acquires the skills necessary to produce a consistent result using trial and error. For the transitioning surgeon, it is particularly difficult to control the plane and speed at which the keratome blade enters the anterior chamber. Variables such as lateral movement due to eye movement, tremor, or other causes can result in incisions that vary in size, shape, and integrity, and may affect the final visual outcome. The present invention eliminates the need for freehand surgery, thereby rendering such variables less significant for the surgeon-in-training.
In the accomplished surgeon's hands, the described freehand corneal incision has become the state of the art incision for performing cataract surgery. Because of the possible complications associated with any surgical training, a large number of surgeons have chosen not to adopt this new technique. The present invention, however, comprises a fixation device coupled with a surgical blade guide, which enables surgeons to make the transition to corneal incisions while greatly reducing or eliminating the possible complications associated with this transition.
Even experienced freehand eye surgeons encounter the common problem of overshooting when introducing the blade into the anterior chamber. Overshooting is due to diminished resistance. When the blade begins to enter the anterior chamber, resistance is lost as the blade moves from a dense media, corneal tissue, into a less dense media aqueous humor. Inability to recover from the sudden loss of resistance causes the blade to go beyond the ideal mark. This creates a rectangular incision, not a trapezoid. The desired incision is, ideally, trapezoidal in shape; that is, narrow distally and wider proximally, so that an instrument inserted into the cornea through the incision may be manipulated without causing stria or stretching the corneal tissue. The incision guide of the present invention eliminates the problem of overshooting.
Prior art instruments include fixation devices and fixation devices coupled with surgical blades. Such instruments were designed to be used in radial keratotomy (a procedure used to correct myopia) and keratectomy (a procedure used to remove a portion of the cornea), but not for cataract surgery or entry into the anterior chamber. Although these instruments are intended to make precise and reproducible incisions, they differ in purpose and design from that of the present invention. The object of the prior art instruments is to either prevent entering the anterior chamber while making arcuate or radial incisions of varying depths or to completely remove a segment of the cornea. Prior art inventions are designed to create a pivoting or dragging cutting movement of a surgical blade that makes either an arcuate or radial type incision.
The present invention reproducibly positions the surgical blade at the corneoscleral limbus at the proper angle for an optimal cataract incision and guides the surgical blade while creating a controlled entry into the anterior chamber of the eye. The present invention guides a surgical blade along an axis perpendicular to the cornea and parallel to the iris to create a penetrating longitudinal incision into the cornea. Prior to the present invention, this type of incision could only be produced freehand by an accomplished surgeon with extensive experience.